U.S. patent application number 10/457565 was filed with the patent office on 2004-01-15 for device for integrating demultiplexing and optical channel monitoring.
Invention is credited to Krug, Peter, Pearson, Matt.
Application Number | 20040008987 10/457565 |
Document ID | / |
Family ID | 29736200 |
Filed Date | 2004-01-15 |
United States Patent
Application |
20040008987 |
Kind Code |
A1 |
Pearson, Matt ; et
al. |
January 15, 2004 |
Device for integrating demultiplexing and optical channel
monitoring
Abstract
A method for integrating power monitoring capabilities with
passive demultiplexing operations, utilizing the high-order
diffraction from an optical diffraction grating. The technique
helps avoid insertion loss and polarization dependent loss
penalties, and device size penalties, typically incurred with
optical taps and multiple diffraction gratings. The technique can
also be modified slightly to provide information on channel
wavelength and optical signal-to-noise-ratio, as well as channel
power.
Inventors: |
Pearson, Matt; (Ashton,
CA) ; Krug, Peter; (Nepean, CA) |
Correspondence
Address: |
MARKS & CLERK
P.O. BOX 957
STATION B
OTTAWA
ON
K1P 5S7
CA
|
Family ID: |
29736200 |
Appl. No.: |
10/457565 |
Filed: |
June 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60386717 |
Jun 10, 2002 |
|
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Current U.S.
Class: |
398/43 |
Current CPC
Class: |
G02B 6/12007 20130101;
G02B 6/29385 20130101; G02B 6/0001 20130101; G02B 6/12004
20130101 |
Class at
Publication: |
398/43 |
International
Class: |
H04J 014/00 |
Claims
We claim:
1. A device for integrating demultiplexing and optical channel
monitoring, comprising: a diffraction grating; an input waveguide
providing an optical input to said diffraction grating; a first set
of output waveguides providing optical outputs to said diffraction
grating at a predetermined order of diffraction; and a second set
of output waveguides providing monitor outputs to said diffraction
grating at another order of diffraction different from said
predetermined order of diffraction.
2. A device as claimed in claim 1, wherein said another order of
diffraction is higher than said predetermined order of
diffraction.
3. A device as claimed in claim 2, further comprising a third set
of outputs at a further order of diffraction different from said
predetermined order of diffraction and said another order of
diffraction, said third set of outputs providing monitor outputs to
said diffraction grating.
4. A device as claimed in claim 3, wherein said further order of
diffraction is lower than said predetermined order of
diffraction.
5. A device as claimed in claim 4, wherein said predetermined order
of diffraction is order n, said another order of diffraction is
order n+1, and said further order of diffraction is order n-1.
6. A device as claimed in claim 3, wherein said second set of
output waveguides are positioned at channel locations, and said
third set of waveguides are positioned at between-channel locations
to provide information on inter-channel noise.
7. A device as claimed in claim 1, further comprising a detector
array coupled to said second set of waveguides.
8. A device as claimed in claim 7, wherein said diffraction grating
is an echelle grating.
9. A device as claimed in claim 8, which is in the form of an
integrated optical device.
10. A method of performing demultiplexing and optical channel
monitoring, comprising the steps of: directing an optical input
signal containing multiple channels to a diffraction grating;
receiving reflected and diffracted signals at a first set of output
waveguides providing optical outputs at a predetermined order of
diffraction; and receiving reflected and diffracted signals at a
second set of output waveguides providing monitor outputs at
another order of diffraction different from said predetermined
order of diffraction.
11. A method as claimed in claim 10, wherein said another order of
diffraction is higher than said predetermined order of
diffraction.
12. A method as claimed in claim 11, wherein reflected and
diffracted signals are received at a third set of outputs at a
further order of diffraction different from said predetermined
order of diffraction and said another order of diffraction, said
third set of outputs providing monitor outputs to said diffraction
grating.
13. A method as claimed in claim 12, wherein said further order of
diffraction is lower than said predetermined order of
diffraction.
14. A method as claimed in claim 13, wherein said predetermined
order of diffraction is order n, said another order of diffraction
is order n+1, and said further order of diffraction is order
n-1.
15. A method as claimed in claim 12, wherein said second set of
output waveguides are positioned at channel locations, and said
third set of waveguides are positioned at between-channel locations
to provide information on inter-channel noise.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit under 35 USC 119(e) of
prior U.S. provisional application serial No. 60/386,717 filed Jun.
10, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to the field of photonics, and in
particular to a device for integrating demultiplexing and optical
channel monitoring. The invention is applicable to integrated
optical components, as well as components based on bulk-optics.
[0004] 2. Description of Related Art
[0005] In an optical telecommunications network based on dense
wavelength division multiplexing (DWDM), several closely-spaced
wavelength channels are multiplexed onto a single optical fiber and
transmitted to another system node where the channels are
demultiplexed and detected individually. It is very important in
DWDM networks to monitor the power in each wavelength channel, as
well as other channel information, such as wavelength and optical
signal to noise ratio (OSNR), which can vary significantly from
channel to channel due to wavelength-dependent amplification or
loss.
[0006] This monitoring is often performed at system nodes
immediately before the main signal is demultiplexed. This is
typically accomplished by tapping a small fraction of the signal
(1% to 5%) off the main transmission line before the demultiplexer.
These two signals, the "main" signal and the "monitoring" signal,
are then sent to separate demultiplexers and separated into their
individual wavelengths. The monitoring channels pass to a detector
array for measuring the power in each channel, while the main
signals split into individual optical fibers for coupling to their
individual receivers or, for example, variable optical attenuators.
This typical functionality is illustrated in FIG. 1. An input
signal is input to an optical tap 1, which splits the signal into a
first portion containing 97% of the light that goes to a
demultiplexer 2 providing the optical outputs. The tap passes 3% of
the light to a demultiplexer 3 that provides outputs that a
detected by a detector array 4.
[0007] A key product focus for integrated optic and bulk-optic
component manufacturers is integration of multiple functions into a
single module. For example, it would generally be desirable to
integrate an optical demultiplexer with an optical channel monitor,
including the 1% optical tap. Such a device would accomplish the
functionality illustrated in FIG. 1.
[0008] One major difficulty with this approach is that in
integrated optics, optical taps often exhibit a polarization
dependent loss (PDL), a major problem for all telecommunications
components. Also, it is difficult to manufacture even a single
optical demultiplexer on a single chip. The functionality
demonstrated in FIG. 1 requires two demultiplexers. Furthermore,
all of the components need to be individually temperature
controlled. Integrating three building blocks into a common device
results in a large device that is difficult to manufacture and has
potential PDL problems.
SUMMARY OF THE INVENTION
[0009] According to the present invention there is provided a
device for integrating demultiplexing and optical channel
monitoring, comprising a diffraction grating; an input waveguide
providing an optical input to said diffraction grating; a first set
of output waveguides providing optical outputs to said diffraction
grating at a predetermined order of diffraction; and a second set
of output waveguides providing monitor outputs to said diffraction
grating at another order of diffraction different from said
predetermined order of diffraction.
[0010] The extra order of diffraction is normally higher than the
predetermined order of diffraction providing the optical outputs.
In a preferred embodiment a further set of waveguides are provided
to receive a further order of diffraction. These can be used for
measuring, for example, inter-channel noise.
[0011] This invention thus describes a method for integrating the
functions of optical demultiplexing and optical tapping, in order
to manufacture the functionality demonstrated in FIG. 1, but with
the use of no optical tap, and with only a single optical
demultiplexer. Also, the invention does not generally induce any
additional optical loss to the system, and in fact can operate
without tapping the typical 1%-5% off the main optical fiber. It
can also substantially eliminate the polarization dependent loss
that can often accompany an optical tap.
[0012] The invention is applicable to integrated optics, but also
to devices based on bulk-optic diffraction gratings.
[0013] In a broad aspect, therefore, the invention uses the light
diffracted into higher orders of the grating, which is typically
just the source of insertion loss in the device. This light that is
diffracted into higher orders is a fixed percentage of the incoming
light, and is precisely the same wavelength as the main signal, and
contains the same information as the main signal, albeit at a much
lower intensity.
[0014] The light can be collected and sent to a detector array,
which after calibration with a known source can provide information
such as the optical power in each channel of the system. Virtually
all demultiplexers rely on a diffractive element, and virtually all
diffractive elements diffract light into higher orders. Designers
typically try to minimize the amount of light diffracted into
higher orders (to minimize optical loss in the main signal), but it
is extremely difficult to eliminate entirely, making the invention
suitable for a wide array of applications. This includes Echelle
Grating demultiplexers, Arrayed Waveguide Grating demultiplexers,
and bulk optic diffraction grating demultiplexers.
[0015] The monitor outputs, i.e. those positioned to collect the
light from higher orders, can be positioned on the channel grid and
monitor the channels at channel center, in the same way as the
light from the main signal is collected at the demultiplexer
output. However, with a slight modification to the above design,
the monitor outputs can be positioned off-center, or be composed of
a split-waveguide output, which means different orders can be
received to deduce different information about the main optical
signal. This type of information could include the monitoring of
channel wavelength, and optical signal to noise ratio, as well as
channel power.
[0016] In a further aspect the invention provides a method of
performing demultiplexing and optical channel monitoring,
comprising the steps of directing an optical input signal
containing multiple channels to a diffraction grating; receiving
reflected and diffracted signals at a first set of output
waveguides providing optical outputs at a predetermined order of
diffraction; and receiving reflected and diffracted signals at a
second set of output waveguides providing monitor outputs at
another order of diffraction different from said predetermined
order of diffraction.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The invention will now be described in more detail, by way
of examples, with reference to the accompanying drawings, in
which:--
[0018] FIG. 1 is a schematic drawing showing the functionality
required for integrating optical demultiplexing with optical
channel monitoring;
[0019] FIG. 2 is a practical layout of an Echelle Grating
demultiplexer designed with monitor outputs positioned at the foci
of the higher-order diffraction; and
[0020] FIG. 3 is a practical layout of an Arrayed Waveguide Grating
(AWG) demultiplexer designed with monitor outputs positioned at
both the order n+1 and order n-1 foci (The n+1 and n-1 outputs can
be off-grid in order to monitor extra information beyond just
power, such as wavelength and OSNR).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE NO. 1
[0021] In the embodiment of the invention shown in FIG. 2, the
components are integrated into a single device. An optical signal
10 consisting of many different wavelength channels is input to the
input waveguide at A. Optical signal 10 travels through the input
waveguide 11, and then spreads out laterally to fill the echelle
diffraction grating 12 at B. The diffraction grating 12 reflects
and diffracts the light back to a first set of several different
output waveguides 13, located at C, based on wavelength. This is
termed the order n of the diffracted light.
[0022] At the same time, a small fraction of the main signal is
reflected and diffracted into a higher order, termed "order n+1",
which is focused onto a second set of monitor output waveguides 14
at position D. Positions C and D are located at the foci of the
diffraction grating for their respective orders.
[0023] The main optical signal is routed off the chip from C to
positions E, where it is coupled to an array of optical fibers.
[0024] The monitoring signal is routed off the chip from D to
position F, where it is coupled to an array 15 of optical
detectors.
[0025] This configuration has several advantages. The single device
shown in FIG. 2 accomplishes the functionality illustrated in FIG.
1, but is a single component, versus the three components
illustrated in FIG. 1. This leads to enormous reductions in
assembled device cost. The main optical signal is demultiplexed
with no significant additional loss or PDL from an optical tap.
This results in improved performance at the system-level as well.
The monitoring signal is created from the higher-order diffraction,
with no additional PDL from an optical tap, and no fiber coupling
between separate components. The single device shown in FIG. 2
replaces the three components illustrated in FIG. 1, and combines
them onto a small optical chip. This also reduces the footprint and
improves the reliability of the completed module. The optical chip
illustrated in FIG. 2 can be temperature controlled using a single
heater/cooler. The use of separate demultiplexers, as illustrated
in FIG. 1, implies roughly twice the power consumption of the new
invention. The invention leads to a significant reduction in power
requirements.
EXAMPLE NO. 2
[0026] In the embodiment shown in FIG. 3 an optical signal 10
consisting of many different wavelength channels is input to the
input waveguide 11 at A. The device operation is identical to that
described in Example No. 1, with the main optical signal being
demultiplexed and output through order n. However, in this example
there are also monitor output waveguides 16 positioned to collect
light of order n+1, as well as n-1. The monitor output waveguides
14 for order n+1 can be identical to those described in Example No.
1, positioned on-grid at channel center, and provide information on
the power in each channel. The monitor outputs for order n-1,
however, can be positioned off-grid, e.g. between channels, and
provide information on the inter-channel noise.
[0027] The outputs can also be designed so that the ratio between
complementary detectors is a known function of wavelength, which
allows the device to monitor the wavelength of each channel. This
can be accomplished, for example, by using the technique described
in U.S. Pat. No. 6,339,662, entitled "Wavelength stabilized planar
waveguide optical devices incorporating a dispersive element", the
contents of which are herein incorporated by reference, or by other
similar techniques.
[0028] The advantages of this configuration include all the
advantages listed for Example No. 1. In addition, wavelength/OSNR
measurements are made possible with no moving parts.
[0029] Typically, wavelength and OSNR monitoring techniques often
involve devices with moving parts such as tunable filters, which
often exhibit reliability issues and have very slow scan times. The
invention described here allows the monitoring of a signal at
several positions on or off grid, all measured simultaneously. This
results in a device with no moving parts, with a very fast scan
time.
[0030] The integrated photonics devices can be made using silica
technology in a manner known per se.
[0031] It will be appreciated by one skilled in the art that many
other variants of the invention are possible within the scope of
the appended claims.
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